1. Field of the Invention
The present invention relates to an antenna device that includes a magnetic substance and a coil conductor, a wireless communication device that includes the antenna device, and a method of manufacturing the antenna device.
2. Description of the Related Art
Japanese Patent No. 4821965 discloses an antenna device having a layered structure in order to realize in a small area an antenna equipped with a magnetic substance, the antenna device performing short-range wireless communication such as Near Field Communication (NFC). By using such a layered structure, the aperture diameter of an antenna coil can be changed only by varying the number of layers, and a coil conductor surface and a surface on which a circuit board is mounted can be arranged to overlap with each other in a plan view, which leads to various advantages such as space saving.
However, in order to manufacture the antenna device having a multilayer structure as disclosed in Japanese Patent No. 4821965, it is necessary to laminate a sheet obtained by mixing magnetic filler with a binder and printing an electrode on the sheet, and co-firing of the sheets integrally. While the sintering temperature of the magnetic substance is not less than 1000° C., however, the firing temperature of silver is approximately 800° C. to 900° C., so that the firing temperature cannot be set to a high temperature of 900° C. or higher. As a result, the magnetic substance is not sintered completely and cannot obtain a favorable material characteristic (a high permeability and a low magnetic loss characteristic), which has been a factor in not being able to obtain a favorable antenna characteristic.